Dynamic nuclear polarization is a technique which has attracted increasing interest in recent years. Methods for dynamic nuclear polarization are described, for example, in WO-A-1999/035508, WO-A-2002/037132, and WO-A-2011/026103, the contents of which are incorporated herein by reference. The essence of the technique is to carry out a magnetic resonance investigation on a nuclear spin system (typically 13C or 15N) of which the spin polarization levels have been perturbed from their equilibrium values prior to a nuclear magnetic resonance investigation, and thereby enhance the sensitivity of the investigation. The perturbation of the spin polarization levels is achieved by interaction between an electron spin resonance transition and a nuclear spin system.
In the DNP experiment described in WO-A-1999/035508, a hyperpolarized solution of a high T1 agent is produced by dissolving a hyperpolarized solid sample of the high T1 agent in a physiologically tolerable solvent. The hyperpolarization of the solid sample is effected by means of a polarizing agent, which may be at least partially separated from the high T1 agent after use. The sample is then administered, for example by injection, to a patient, and is then irradiated using a second rf to excite nuclear spin transitions in selected nuclei e.g. the MR imaging nuclei of the high T1 agent. Magnetic resonance signals are detected and NMR spectral data, an image, dynamic flow data, diffusion data, perfusion data, physiological data may be measured. The long T1 results in persistence of the nuclear spin polarization, allowing significantly enhanced sensitivity in the NMR determination to be achieved over a useful time period.
One disadvantage of this approach is the relatively long polarization time (typically of the order of thirty minutes or more).